[Public WebGL] Resolve MSAA depth?

Mr F [email protected]
Thu Jan 19 06:38:21 PST 2017


I know and I'm not doing deferred, but rather more simple depth-dependent
effects in forward, which work quite fine with blitFramebuffer depth
(except the current performance issue). If I can't write to R32F with MSAA
though, I can only write encoded RGBA8 values, and these got averaged, they
become useless.

On 19 January 2017 at 17:34, Florian Bösch <[email protected]> wrote:

> Note that averaged (MSAA'ed) colors at the borders and a single depth
> value for the pixel produces noticable artifacts when shading as a deferred
> step (using the depth for light calculations like area of influence of a
> deferred light).
>
> Most deferred renderers don't do MSAA rendering for that reason (and
> because of performance) and use alternative approaches to AA'ing that
> operates on the output once all lighting calculations are done.
>
> On Thu, Jan 19, 2017 at 3:28 PM, Mr F <[email protected]> wrote:
>
>> Furthermore, rendering depth to a separate RT (using drawBuffers) doesn't
>> make much sense, because the samples are averaged (only needs 1st sample,
>> and that's what blit was supposed to do).
>>
>> On 19 January 2017 at 16:46, Mr F <[email protected]> wrote:
>>
>>> Hmm seems like ANGLE is not able to render MSAA R32F color as well? So
>>> I'll have to use RGBA8 encoded depth WebGL1-style again.
>>>
>>> On 19 January 2017 at 00:02, Mr F <[email protected]> wrote:
>>>
>>>> I've just posted a possible solution to this issue there.
>>>>
>>>> On 18 January 2017 at 01:08, Jamie Madill <[email protected]> wrote:
>>>>
>>>>> Aha yes.
>>>>>
>>>>> Long story short, I couldn't get multisampled resolve (aka blit from
>>>>> multisample to single-sampled textures) working with a shader. I spent a
>>>>> fair bit of time on this. Sorry about this, but for now it's a slow path.
>>>>> Feel free to comment on the issue I just opened: anglebug.com/1710. I
>>>>> tried this a few different ways but always ended up with a blank texture
>>>>> and nothing being written.
>>>>>
>>>>> Not sure what to suggest other than trying to use a non-depth texture
>>>>> for the same effect if possible.
>>>>>
>>>>> On Tue, Jan 17, 2017 at 4:27 PM, Mr F <[email protected]> wrote:
>>>>>
>>>>>> Here's a tiny example: http://geom.io/testResolveDepth/index.html
>>>>>> It blits MSAA R11G11B10 + 32F depth into 2 non-multisampled textures.
>>>>>>
>>>>>>
>>>>>> On 18 January 2017 at 00:23, Mr F <[email protected]> wrote:
>>>>>>
>>>>>>> I'm talking about multisampled blit though
>>>>>>>
>>>>>>> On 17 January 2017 at 23:03, Jamie Madill <[email protected]>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Non-multisample depth blit by itself should use a shader.. but we'd
>>>>>>>> need a small repro case to verify. Let me know if you can pull one together
>>>>>>>> and I'll look.
>>>>>>>>
>>>>>>>> On Tue, Jan 17, 2017 at 2:39 PM, Mr F <[email protected]>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> I understand depth/stencil complications. Are you sure 32F depth
>>>>>>>>> blits are never CPU-bound? There's a weird issue right now with it taking
>>>>>>>>> large chunk of performance, although only in FF Nightly (Chrome is fine). I
>>>>>>>>> wonder if some older versions of ANGLE did CPU copy for D32F?
>>>>>>>>>
>>>>>>>>> On 17 January 2017 at 22:28, Jamie Madill <[email protected]>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> Blit is core in GLES 3, so we need to emulate some of the
>>>>>>>>>> depth/stencil blits to support GLES 3 at all. Such is the nature of what
>>>>>>>>>> ANGLE does.
>>>>>>>>>>
>>>>>>>>>> It's something that is predictable from ANGLE's point of view,
>>>>>>>>>> but I understand it might be unclear from the app's point of view. Stencil
>>>>>>>>>> bits in particular are difficult, and multisample depth/stencil. We're
>>>>>>>>>> working on making this more visible - one thing is that it'll show up in
>>>>>>>>>> Chrome's about:gpu page. Ideally it could show up in some debugging log
>>>>>>>>>> visible to javascript.
>>>>>>>>>>
>>>>>>>>>> On Mon, Jan 16, 2017 at 11:37 AM, Mr F <[email protected]>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>> So it seems like ANGLE sometimes implements blit on CPU (!):
>>>>>>>>>>> https://github.com/google/angle/blob/master/src/libANGL
>>>>>>>>>>> E/renderer/d3d/d3d11/Blit11.cpp#L240
>>>>>>>>>>>
>>>>>>>>>>> Which gives huge slowdowns without really telling why and being
>>>>>>>>>>> able to predict it. If on some platform some blit is not possible, maybe we
>>>>>>>>>>> should just throw an error, disable it, make it an extension or something?
>>>>>>>>>>> CPU blit is pure evil.
>>>>>>>>>>>
>>>>>>>>>>> On 1 December 2016 at 15:50, Mr F <[email protected]> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> OK, sorry for bothering - must be my mistake somewhere. Made it
>>>>>>>>>>>> work while preparing the test case :)
>>>>>>>>>>>>
>>>>>>>>>>>> On 30 November 2016 at 23:03, Jamie Madill <
>>>>>>>>>>>> [email protected]> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> Yes, a reproduction / test case would be awesome, thanks.
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Tue, Nov 29, 2016 at 9:20 PM, Jeff Gilbert <
>>>>>>>>>>>>> [email protected]> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> FWIW, the spec says pretty explicitly that BlitFramebuffer
>>>>>>>>>>>>>> should be
>>>>>>>>>>>>>> functional for depth->depth blitting, as long as the formats
>>>>>>>>>>>>>> match,
>>>>>>>>>>>>>> etc etc.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> GLES 3.0.5 p198:
>>>>>>>>>>>>>> If the
>>>>>>>>>>>>>> source formats are depth values, sample values are resolved
>>>>>>>>>>>>>> in an
>>>>>>>>>>>>>> implementation-
>>>>>>>>>>>>>> dependent manner where the result will be between the minimum
>>>>>>>>>>>>>> and maximum
>>>>>>>>>>>>>> depth values in the pixel.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Tue, Nov 29, 2016 at 8:16 PM, Kenneth Russell <
>>>>>>>>>>>>>> [email protected]> wrote:
>>>>>>>>>>>>>> > Could you make any test case available? Do you have any
>>>>>>>>>>>>>> other platforms
>>>>>>>>>>>>>> > (Mac, Linux) to test on? You could also try launching
>>>>>>>>>>>>>> Chrome with the
>>>>>>>>>>>>>> > command line argument --use-angle=gl to see the difference
>>>>>>>>>>>>>> between ANGLE's
>>>>>>>>>>>>>> > D3D11 and OpenGL backends.
>>>>>>>>>>>>>> >
>>>>>>>>>>>>>> >
>>>>>>>>>>>>>> > On Tue, Nov 29, 2016 at 12:42 PM, Mr F <
>>>>>>>>>>>>>> [email protected]> wrote:
>>>>>>>>>>>>>> >>
>>>>>>>>>>>>>> >> I'll try to prepare a clean test case soon. I'm on the
>>>>>>>>>>>>>> latest Chrome
>>>>>>>>>>>>>> >> Canary/Win 7/GTX970. Both source and destination are 32F.
>>>>>>>>>>>>>> What I mean by
>>>>>>>>>>>>>> >> "blank" actually looks like a solid red color, which seems
>>>>>>>>>>>>>> to be uniform
>>>>>>>>>>>>>> >> 1,0,0, no matter how close/far I'm from any geometry.It's
>>>>>>>>>>>>>> good to know that
>>>>>>>>>>>>>> >> it is supposed to work - maybe just my mistake somewhere,
>>>>>>>>>>>>>> although I tested
>>>>>>>>>>>>>> >> it heavily. The source buffer is created and attached using
>>>>>>>>>>>>>> >>
>>>>>>>>>>>>>> >> renderbufferStorageMultisample(gl.RENDERBUFFER, 4,
>>>>>>>>>>>>>> gl.DEPTH_COMPONENT32F,
>>>>>>>>>>>>>> >> width, height)
>>>>>>>>>>>>>> >> framebufferRenderbuffer(gl.FRAMEBUFFER,
>>>>>>>>>>>>>> gl.DEPTH_ATTACHMENT,
>>>>>>>>>>>>>> >> gl.RENDERBUFFER, msaaBuffer)
>>>>>>>>>>>>>> >>
>>>>>>>>>>>>>> >> and the destination created and attached to another
>>>>>>>>>>>>>> framebufer with
>>>>>>>>>>>>>> >>
>>>>>>>>>>>>>> >> texImage2D(gl.TEXTURE_2D, 0, gl.DEPTH_COMPONENT32F, width,
>>>>>>>>>>>>>> height, 0,
>>>>>>>>>>>>>> >> gl.DEPTH_COMPONENT, gl.FLOAT, null)
>>>>>>>>>>>>>> >> framebufferTexture2D(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT,
>>>>>>>>>>>>>> gl.TEXTURE_2D,
>>>>>>>>>>>>>> >> tex, 0)
>>>>>>>>>>>>>> >>
>>>>>>>>>>>>>> >> The blit is performed like this:
>>>>>>>>>>>>>> >> bindFramebuffer(gl.READ_FRAMEBUFFER, msaaFBO)
>>>>>>>>>>>>>> >> bindFramebuffer(gl.DRAW_FRAMEBUFFER, resolveFBO)
>>>>>>>>>>>>>> >> blitFramebuffer(0, 0, width, height, 0, 0, width, height,
>>>>>>>>>>>>>> >> gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT, gl.NEAREST)
>>>>>>>>>>>>>> >>
>>>>>>>>>>>>>> >> On 29 November 2016 at 17:51, Jamie Madill <
>>>>>>>>>>>>>> [email protected]> wrote:
>>>>>>>>>>>>>> >>>
>>>>>>>>>>>>>> >>> This generally should work. There are tests for this in
>>>>>>>>>>>>>> dEQP's
>>>>>>>>>>>>>> >>> dEQP-GLES3.functional.fbo.msaa and also in the WebGL
>>>>>>>>>>>>>> 2-specific tests in
>>>>>>>>>>>>>> >>> gles3/fbomultisample and I think also fboinvalidate/sub.
>>>>>>>>>>>>>> >>>
>>>>>>>>>>>>>> >>> Note some of these tests are marked as failing on Intel
>>>>>>>>>>>>>> on pretty much
>>>>>>>>>>>>>> >>> all platforms:
>>>>>>>>>>>>>> >>>
>>>>>>>>>>>>>> >>> https://cs.chromium.org/chromi
>>>>>>>>>>>>>> um/src/content/test/gpu/gpu_tests/webgl2_conformance_expecta
>>>>>>>>>>>>>> tions.py?q=webgl2_conform&sq=package:chromium&l=118
>>>>>>>>>>>>>> >>>
>>>>>>>>>>>>>> >>> Mr F, what platform are you on, and which vendor?
>>>>>>>>>>>>>> >>>
>>>>>>>>>>>>>> >>> On Mon, Nov 28, 2016 at 10:34 PM, Kenneth Russell <
>>>>>>>>>>>>>> [email protected]> wrote:
>>>>>>>>>>>>>> >>>>
>>>>>>>>>>>>>> >>>> I'm pretty sure this should either work, or generate an
>>>>>>>>>>>>>> OpenGL error.
>>>>>>>>>>>>>> >>>> OpenGL ES 3.0.5 section 4.3.3 "Copying Pixels" says
>>>>>>>>>>>>>> BlitFramebuffer
>>>>>>>>>>>>>> >>>> generates INVALID_OPERATION if the mask includes
>>>>>>>>>>>>>> DEPTH_BUFFER_BIT or
>>>>>>>>>>>>>> >>>> STENCIL_BUFFER_BIT, and the source and destination depth
>>>>>>>>>>>>>> and stencil buffer
>>>>>>>>>>>>>> >>>> formats don't match.
>>>>>>>>>>>>>> >>>>
>>>>>>>>>>>>>> >>>> It looks like there are extensive tests of resolving
>>>>>>>>>>>>>> multisampled depth
>>>>>>>>>>>>>> >>>> buffers to single-sampled ones, but I'm not sure about
>>>>>>>>>>>>>> resolving to a depth
>>>>>>>>>>>>>> >>>> texture. Do you have a test case? What platform are you
>>>>>>>>>>>>>> on (can you provide
>>>>>>>>>>>>>> >>>> about:gpu if you're running Chrome)?
>>>>>>>>>>>>>> >>>>
>>>>>>>>>>>>>> >>>> -Ken
>>>>>>>>>>>>>> >>>>
>>>>>>>>>>>>>> >>>>
>>>>>>>>>>>>>> >>>>
>>>>>>>>>>>>>> >>>> On Sat, Nov 26, 2016 at 12:26 PM, Mr F <
>>>>>>>>>>>>>> [email protected]> wrote:
>>>>>>>>>>>>>> >>>>>
>>>>>>>>>>>>>> >>>>> The docs are a bit unclear on that. Is it possible to
>>>>>>>>>>>>>> use
>>>>>>>>>>>>>> >>>>> blitFramebuffer to get current MSAA depth buffer into a
>>>>>>>>>>>>>> non-MSAA depth
>>>>>>>>>>>>>> >>>>> texture? The color buffer is resolved nicely, however
>>>>>>>>>>>>>> the depth is just
>>>>>>>>>>>>>> >>>>> blank, and no error is generated - wondering if it's
>>>>>>>>>>>>>> the expected behaviour.
>>>>>>>>>>>>>> >>>>> Depth format is DEPTH_COMPONENT32F.
>>>>>>>>>>>>>> >>>>
>>>>>>>>>>>>>> >>>>
>>>>>>>>>>>>>> >>>
>>>>>>>>>>>>>> >>
>>>>>>>>>>>>>> >
>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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